Adjustable airlift pump



April 10, 1962 J. CUNETTA 3,028,817

ADJUSTABLE AIRLIFT PUMP Filed May 5, 1958 INVENTOR.

BY WWW 9%.

States atent 3 ,628,817 Patented Apr. 10, 1962 Airlift pumps have been known for many years and have been recognized as much more desirable for some situations than the more common pumps with moving parts. When liquid only needs to be lifted a short distance, it can quite often be pumped most efliciently by an airlift pump.

In a typical airlift pump situation, a vertical updraft tube may extend down perhaps 12 or 13 feet below the level of the liquid to be pumped. Near the bottom of the updraft tube, air is liberated within the tube so that the air can rise up through the tube. The buoyancy of the air causes the water in the tube to be raised with it, the actual raising force of course coming from the pressure of the liquid outside of the tube. There must be enough air in the column of water within the tube at all times so that the density within the tube is enough less than the density of the liquid outside of the tube so that even when the water is being raised to the required height the pressure it creates at the bottom of the tube is less than the pressure outside the tube at the same depth. If we consider successively increased heights to which the liquid must be raised, the eflic-iency becomes lower and lower, unless the tube is correspondingly extended downwardly. Unless the liquid supplied to the tube seeks a level nearly seventy percent of the height from air liberation to the discharge surface level, the efliciency may drop so low as to make this type of pumping undesirable.

Increasing the eificiency of an airlift pump by only a small percentage is sometimes quite important. For example, if airlift pumps are used for pumping tremendous quantities of liquid, as in pumping the main flow of sewage from one treatment unit to another, every percent of increased efiiciency may result in a saving of relatively great sums of money in the course of a year. Design features which only minutely increase the efficiency of an airlift pump when it is operating With extremely low lift where its efiiciency is highest, may become much more important when the lift is large enough so that airlift pumps tend to operate at a considerably reduced efiiciency. It is the purpose of the present invention to provide an airlift pump with exceptionally high efficiency.

According to an important feature of an application I filed recently, the updraft tube of the airlift pump is made of substantially larger cross sections in the upper part of its length than in the lower part of its length. This has been found to increase the efficiency quite substantially. The updraft tube should extend nearly the full height to which the water is to be raised so as to retain an unimpaired low density as high as possible. But it should be enough submerged to release the pumped liquid without wastefully lifting it substantially above the liquid level in the receiving basin. Preferably a baflle plate positioned at or just above the liquid level, over the upwardly open tube, confines the flow area from the tube slightly. This tends to minimize surges which under some conditions cause a decreased overall efiiciency in the airlift pump. The surges themselves represent moments of increased efiiciency.

According to an additional concept of the present invention, another aid to efficiency is provided in the form of means for adjusting the height of liberation of air in the updraft tube. Preferably the liberating head is carried by a pipe extending down into the tube through the opening at the top thereof, and adjusting this tube adjusts the height of discharge.

This adjustability permits lowering the air head as deep 2 as the available air pressure will permit. This is especially important when the airlift pump is supplied by the same air compressor or blower mainly used for supplying another unit, such as a sewage aeration tank. For efliciency the blower should compress only to the pressure required to supply the other unit. If the air lift air head should be placed a half inch too low, it would not dependably liberate enough air to cause the airlift pump to perform its pumping job.

Additional objects and advantages of the invention will be apparent from the following description and from the drawings.

Designation of Figures FIGURE 1 is a vertical sectional view through one form of air airlift pump chosen for illustration of the invention showing also its relationship to another tank.

FIGURE 2 is a fragmentary vertical sectional view of a modified form of airlift pump.

General Description Although the following disclosure offered for public disaid toward this purpose, as it is these that meet the requirement of pointing out the parts, improvements, or combinations in which the inventive concepts are found.

An airlift pump comprises essentially a vertical updraft tube 11 having its intake 12 or an intake connection at its lower end and having its discharge end 13 at the top either open, as shown, or in communication with a pipe. llf it is not open, there is usually .some'rneans provided for the separation of air from liquid.

An air liberating head 14 is positioned to discharge air deep within the tube or near the bottom thereof. In the past the discharge device has often been a collar surrounding the tube and liberating air through the tube.

In the illustrated form the air liberating head 14 is car ried by a pipe 16 extending down through the open discharge-opening 15 of the updraft tube 11. This construction has the advantage that by providing suitable arrangements, the tube 16 with its head 14 may readily be raised to permit inspection of the head 14 and its cleaning if necessary. The suitable arrangements may include positioning the tube 16 by a readily releasable clamp 18 and supplying the tube 13 with compressed air through a hose long enough to permit removal of the tube 16 or through a readily separable coupler which permits separation of the tube 16 from the air supply source.

Adjustable Depth of Air Liberation 7 ing the depth of head 14. This is especially important if it is supplied with air from a source, represented by supply main 20 which also supplies much larger quantities of air to other equipment at a pressure not much higher than that required for head 14.

For example, the other equipment may be aeration tanks of which tank 21 is one, having hundreds of air liberating nozzles 22. Any compressing of air for supply pipe Zil greater than needed for proper operation of nozzles 22 would be a tremendous waste of power in the course of a year. Flexible hose 23 permits location of head 14 as deep as the air pressure in supply pipe 20 will permit. Without adjustability of height of head 14 designers will tend to provide a wide margin of safety. This means placing the head 14 perhaps three inches higher than ideal, to be sure the available air pressure will put enough air through it. Such three inches would cause a loss of efficiency in the airlift pump, as compared to the maximum operable submergence, here assumed to be three inches more. It may be convenient to provide a height adjustment clamp such as collar 31 with hand screw 3% which can remain in position when pipe 16 is withdrawn by opening clamp 18.

Some means should be provided for centering the lower end of pipe 16. As illustrated, head 14 comes close enough to the tube 26 to do so, the head having four perforated or porous arms. If the head were smaller, fins could be provided.

The tube 11 terminates with a discharge opening 15 discharging into a receiving basin 17, from which the liquid flows through a pipe or channel 19.

Enlarged Cross Section As seen in FIG. 1, practically the upper third of the updraft tube 11 is of larger diameter, and hence larger cross section, than is the lower or main portion 26 of the tube 11. Preferably the enlargement occurs quite gradually, the enlarging portion 27 being shown in the form of an inverted truncated cone, the diameter of which increases upwardly rather slowly. Although this cone may extend all the way to the open top of this tube, there is preferably located above it a section 28 of cylindrical tubing of the same diameter as the upper end of the enlarging section 27. In most applications it is contemplated that the tube 28 will extend in cylindrical form all the way to the top of the airlift tube as seen in FIG. 2, perhaps with a separable top section that can be replaced for different heights. However, there may be some advantage in a further tapering enlargement or hell as seen at 29 in FIG. 1.

There could be one conical enlargement all the way from the top of the main cylindrical tube 26, or even from the level of air liberating head 14, to the open upper end of the airlift tube 11, but since the normal method of manufacture requires the use of separate sections it is at present preferred that some portions be cylindrical, if only for economy of construction.

Both of the constructions of FIGS. 1 and 2 produce a substantial increase in the efficiency of the airlift pump as compared to using an updraft tube of uniform cross section. One of the reasons that the increasing cross section increases the efliciency of the pump is that the air bubbles in the tube expand as they rise and are subject to reducing pressure. It follows that a gallon of liquid mixed with air bubbles requires more and more space as it rises. Hence if the mixture including a gallon of liquid flowed at a given speed in the lower part of tube 16 it would have to flow faster in the upper part of tube 16, if of uniform cross section, in order to get its increased volume past a given point in the same length of time. Accordingly, it is desirable that the amount of enlargement of the cross sectional area of the tube be at least sufficient to take care of the increased volume due to the expanding of the air with decreasing pressure.

As a matter of fact, more increase of area than this is preferred. The upward speed of the water at the discharge end 13 of the airlift pump represents energy of which little or no use is made, and this in turn is some wasting of power. By enlarging the cross sectional area of the tube more than enough to accommodate the expansion of the bubbles, there is some recovery of this velocity energy, or some reduction in the wasted upward velocity of the water at discharge.

Too much enlargement of the cross sectional area upwardly would cause some loss of lifting action. For example, if the enlargement should be so great as to leave the rising column of air and water mixture substantially unconfined, more debubbled liquid would find its way into the stream and would decrease the proportion of air to water in the lift stream with loss of lifting action. Even smaller sizes than this might permit too much air to escape, leaving a denser mixture. Also, for reasons of economy of material in the structure, it is undesirable to increase the size beyond the smallest size which will attain maximum efficiency. Indeed, even maximum efficiency is not likely to be economically wise inasmuch as a minutely smaller diameter may save material costs with a loss of efficiency so slight that it would be almost more theoretical than real.

With submergence of the tube around 12 feet an increase of cross sectional area to double that of the main or lower tube has been found to be a suitable enlargement.

If costs were not a factor, the enlargement would ideally begin lower than has been indicated. Because of the cost factor, some designers may have it begin higher than indicated in FIG. 1. FIG. 2 shows a slightly less gradual enlargement. Here the enlargement to twice the lower cross sectional area is made in a height of approximately the diameter of the lower tube. An enlargement represented by an angle of 15 from the vertical of the conical sides is believed to be about the most abrupt enlargement that should be used without careful tests for each installation. Greater abruptness, unless with more expensive streamline curves is likely to cause a hydraulic drag, and objectionable turbulence, and could cause coalescence of the bubbles and loss of lifting power. For high efiiciency an expansion section in which the angle of the walls to the vertical is as small as 10 is preferred. The lower it is, unless close to header 14, the greater the efficiency. It is preferably spaced below the top of tube 11 a length at least equal to the diameter of tube 26. If more abrupt enlargement is used, as in FIG. 2, greater spacing of its top from the discharge outlet 15 is preferred.

The 10 and 15 figures can be expressed as radial enlargement rates of approximately 18% and 27% respectively, as compared to the height through which the increase occurs. Present excellent experience has been with even more gradual expansion, approximately 5 (.09%) or less. It would be wise to stay within this limit unless tests confirm the assumption that 10% gives as good results.

Bafile Plate and Depth of Discharge Preferably a baflie plate 35 is located above the dis charge of airlift tube 11, the baffle plate being substan* tially larger in diameter than the discharge opening 15 of the tube 11. Unless the preferred spacing of this invention is used, the spacing of the opening 15 below this baffle plate may not make much difference provided the opening is fairly close below the surface to protect the airlift effect as long as possible without wasting lifting effort, and assuming the spacing avoids a constricting efiect. The baffle may thus serve mainly as a splash plate to prevent the upcoming liquid from splashing out of the receiving basin 17. Under other conditions however it is desirable to locate the opening 15 close enough to the baffle plate 35 so that the baffle will impede the flow from the tube appreciably during abnormal surge conditions. This is desirable when the surges otherwise would be so great as to be followed by an abnormally slack flow, especially if the overall efficiency would be less than a steady flow without the surges. The area of discharge clearance between opening 15 and baffle 35, or the amount of confinement may depend in part on whether the deflected flow has an advantageous direction. If it causes a faster flow from receiving basin 17 this may minutely reduce the amount of lift required and justify slightly greater confinement.

The spacing of the discharge outlet 15 below the liquid level in receiving basin 17 is important. Unless the deflection produces a useful velocity, the opening 15 up should be as far below the surface as possible without increased back pressure. The increase could occur if dehubbled water appears in the uptlow area. A spacing of the discharge opening below the liquid level, and below the baffle 35, desired is approximately one which makes the clearance area between the rim of the discharge opening and the nearest points of the bafile (or the sub-surface flow area if there is no baffle) as small as approximately four times the area in the lower or main portion 26 of the updraft tube.

It may be noted that although it is too early to say that exactly the various areas given are ideal, the area comparisons stated have been made ignoring the small reduction of the area of the tube by the air pipe 16 ex tending down through it. If it were taken into account so as to consider the actual flow area, the enlargement would be to a little more than double and the discharge area between opening 15 and bafiie plate 35 would be a little more than four times the flow area of the tube 11..

Two simple means of adjusting the position of baffle 35 have been shown. In FIG. 1 it is supported by fixed bolts 36 and its position thereon may be varied by nuts above and below it. Although only two bolts 36 are shown, it is contemplated that there would be at least three.

FIG. 2 shows another form of adjusting the position of baffle plate 35, namely by a set screw 38 engaging pipe 16. As a matter of fact, the baffle plate 35 may slide freely on pipe 16, and in some conditions that is preferred, at least if limited in its upward movement, although it is a further feature not claimed by the present applicant as his invention.

The batlie plate 35 may be made in two separable halves which may be bolted or clamped together after assembly around pipe 16.

Sometimes the gas supplied to airlift pumps is some other gas than air, but the difference is not material to pump operation. For this application air is used for convenience as inclusive of any gas.

The ability to adjust and withdraw air assembly including head 14 and pipe 16 makes practical the use of a porous air head, if tests prove such a head provides any greater efliciency than a perforated header. If the head becomes slightly clogged so that it uses up a little more pressure than when clean the head can be raised slightly. When it becomes excessively clogged, it may be withdrawn and cleaned. Porous air diffusion materials are known. One having possible advantages over those commonly used heretofore is sintered metal, as the products of powdered metallurgy are commonly called.

The outlet 15 should be substantially above the floor of the receiving basin 17, at least as such basins have been constructed heretofore. Inasmuch as the outlet 15 is to be located fairly close to the surface, the floor will naturally be substantially lower. In any event, impedance of flow away from outlet 15 should be avoided, and a large cross-sectional area for flow-off is an aid to this.

In case a varying level in the receiving basin is expected, the height of the outlet 15 above its floor may be made adjustable. For example, the upper portion, say the upper half, of that portion of the updraft tube which rises above the fioor of the receiving basin may telescope with respect to the lower portion and be adjustable by nuts on supporting rods which either extend up from the floor or down from a beam. When the cost of this adjustment is not considered justified, but the precise liquid level is not known, the portion of the updraft tube above the floor of the receiving basin may be made in two separable parts so that the upper part could be removed and replaced by a similar portion of different height.

if desired, the upper surface of panel 35 may be shaped to ensure a smooth radial deflection of the liquid with minimum loss of its velocity head.

I claim:

1. An airlift pump including an updraft tube, means for liberating air at a low point in said tube for producing airlift action in said tube when liquid is supplied to it below said means to seek a level well above said means, a discharge outlet in a horizontal plane at the upper end of said tube; said discharge outlet being below the surface level of the liquid into which it is discharging, but close enough to said level so that the annular vertically disposed outward fiow area between said surface level and said outlet is as small as approximately four times the cross-sectional flow area of the tube in the vicinity of the means for liberating air therein, a baffle above the outlet, substantially as large as the outlet, and means locating said baflle approximately at said surface level, to deflect the upflow laterally.

2. An airlift pump including an updraft tube, means for liberating air at a low point in said tube for producing airlift action in said tube when liquid is supplied to it below said means to seek a level well above said means, a discharge outlet at the upper end of said tube; said discharge outlet being below the surface level of the liquid into which it is discharging, but close enough to said level so that the annular vertically disposed outward flow area between said surface level and said outlet is as small as approximately four times the cross-sectional flow area of the tube in the vicinity of the means for liberating air therein, and means substantially as large as said outlet approximately at said surface level upflow laterally.

3. An airlift pump including an updraft tube, means for liberating air at a low point in said tube for producing airlift action in said tube when liquid is supplied to it below said means to seek a level well above said means, a discharge outlet at the upper end of said tube; a bafiie substantially as large as said outlet, means locating the battle opposite the discharge outlet and at least when the pump is operating spaced from it but retained close enough to it to increase the average rate of flow upwardly through the tube due to airlift action over the average rate which would be obtained with the bafile removed.

4. An airlift pump according to claim 3 including a asin into which the updraft tube discharges, said basin having an off-flow passage, both the basin and off-flow passage providing a substantial depth above their bottom surfaces for fiow from the updraft tube, and said updraft tube having its discharge outlet substantially higher than the bottom surfaces.

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